feat: SSH-Agent Support

[zoop-btc]

Hi,

Since I cannot allow ssh password authentication I have added a quick and dirty ssh-agent support for linux and a ssh user override.
I have not implemented anything in windows since it would require multiple source files and I'm not familiar with go. This repo seems to do that so may be a good guideline for future implementation.

This draft is meant for discussion only.

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Relates to #307

[bpg]

Hi @zoop-btc, thanks for contribution!

To be honest, I would skip Windows support for ssh agent for now and add it later if/when it will be requested.

Overall I think this change makes sense.
I've added some other comments, could you please take a look?

[zoop-btc]

I think the pull request is in a good place. However I am unsure how to approach the ssh-host override as it's a per-node setting. Do you think it makes sense to define a map of proxmox-node names => proxmox ssh-hosts inside the provider configuration?
@bpg

[bpg]

Do you think it makes sense to define a map of proxmox-node names => proxmox ssh-hosts inside the provider configuration?

I was thinking about it, but that doesn't looks great in the template though.
Maybe try another option: use existing approach with IP address lookup, but don't stop on the first interface, try them all from the list until connected?

[bpg]

Hey @zoop-btc, do you need a hand with this PR? I can help with testing / implementation of the last piece. Or we can do that in a separate PR.

[zoop-btc]

@bpg I can do it, but since I'm busy I'll only come around to it till late next week. If you want to do it though feel free :)
Also can you stop merging the main branch? I will rebase this branch when I get back to it anyways.

[bpg]

@zoop-btc sorry about all that annoyance, I'm working on a new PVE cluster setup and the agent feature is really helpful for my case, so I used your branch for testing 😅
Yeah, I can continue with this, if you don't mind. Will refrain from pushing until it's done.

[bpg]

Nice work @zoop-btc to put this together!

I've added agent_socket argument and made a few minor tweaks to allow agent functionality on MacOS as well. Also, rebased on main

I'll add you as a co-author when merge the PR